Effect of water vapor on sound absorption in nitrogen at low frequency/pressure ratios

Sound absorption measurements were conducted in N2-H2O binary mixtures at 297°K, over a range of frequency/pressure (f/P) from 0.1–2500 Hz/atm, to study the vibrational relaxation peak of N2 and its location on the f/P axis as a function of humidity. At low humidities the best fit of the reported data to a linear relationship between (f/P)max and humidity yields an intercept of 0.013 Hz/atm and a slope of 2.00×104 Hz/atm⋅mole fraction. The slope is lower than the value of 2.6×104 reported by Chang, Shields, and Bass at higher humidities [J. Acoust. Soc. Am. 62, 577–581 (1977)], but the two sets of data are shown to be mutually consistent by means of a model in which V–V transfer is assumed to provide the dominant relaxation path. The best fit to both sets of data is expressed by the relationship (f/P)max=0.013 +2.0×104 [(1+173h)/(1+133h)]h Hz/atm, h in mole fraction. The reaction rate constants derived from this model are lower than those obtained from extrapolation of previous high-temperature data.